{
  description = "Ultimate Notetaking, Sync & Backup System - NixOS configuration for managing personal data";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    home-manager = {
      url = "github:nix-community/home-manager";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    sops-nix = {
      url = "github:Mic92/sops-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    # Optional: Neovim distribution
    # nixvim = {
    #   url = "github:nix-community/nixvim";
    #   inputs.nixpkgs.follows = "nixpkgs";
    # };
  };

  outputs = { self, nixpkgs, home-manager, sops-nix, ... }@inputs:
    let
      # Supported systems
      supportedSystems = [ "x86_64-linux" "aarch64-linux" ];

      # Helper to generate outputs for all systems
      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;

      # Nixpkgs instantiated for each system
      nixpkgsFor = forAllSystems (system: import nixpkgs {
        inherit system;
        config.allowUnfree = false; # FOSS only
      });

      # Shared modules for all hosts
      sharedModules = [
        ./modules/nb.nix
        ./modules/syncthing.nix
        ./modules/backup.nix
        sops-nix.nixosModules.sops
      ];

      # Create a NixOS configuration for a host
      mkHost = { hostname, system ? "x86_64-linux", extraModules ? [] }:
        nixpkgs.lib.nixosSystem {
          inherit system;
          specialArgs = { inherit inputs; };
          modules = sharedModules ++ [
            ./hosts/${hostname}/configuration.nix
            home-manager.nixosModules.home-manager
            {
              home-manager.useGlobalPkgs = true;
              home-manager.useUserPackages = true;
              # home-manager.users.YOUR_USERNAME = import ./home;
            }
          ] ++ extraModules;
        };

    in {
      # NixOS configurations
      # Uncomment and customize for your hosts:
      #
      # nixosConfigurations = {
      #   desktop = mkHost { hostname = "desktop"; };
      #   laptop = mkHost { hostname = "laptop"; };
      #   server = mkHost {
      #     hostname = "server";
      #     extraModules = [
      #       ./modules/server/forgejo.nix
      #       ./modules/server/immich.nix
      #       ./modules/server/jellyfin.nix
      #     ];
      #   };
      # };

      # One-command setup: nix run .
      apps = forAllSystems (system:
        let
          pkgs = nixpkgsFor.${system};
          setupScript = pkgs.writeShellApplication {
            name = "usync-setup";
            runtimeInputs = with pkgs; [
              git
              jq
              age
              sops
              syncthing
              qrencode
              zbar
              ffmpeg
            ];
            text = ''
              # Find the setup script
              SCRIPT_DIR="''${UNSBS_DIR:-}"
              if [[ -z "$SCRIPT_DIR" ]]; then
                # Try current directory first
                if [[ -f "./setup" ]]; then
                  SCRIPT_DIR="."
                # Try the flake source
                elif [[ -f "${self}/setup" ]]; then
                  SCRIPT_DIR="${self}"
                else
                  echo "Error: Cannot find setup script"
                  echo "Run from the repo directory, or clone it first:"
                  echo "  git clone ssh://git@your-server:2222/you/grapho.git"
                  exit 1
                fi
              fi
              exec "$SCRIPT_DIR/setup" "$@"
            '';
          };
        in {
          default = {
            type = "app";
            program = "${setupScript}/bin/usync-setup";
          };
          setup = {
            type = "app";
            program = "${setupScript}/bin/usync-setup";
          };
        }
      );

      # Development shell with all tools
      devShells = forAllSystems (system:
        let
          pkgs = nixpkgsFor.${system};
        in {
          default = pkgs.mkShell {
            name = "unsbs-dev";

            packages = with pkgs; [
              # Tier 2: Notes & Sync
              nb              # Notebook CLI
              syncthing       # File sync
              unison          # Alternative sync

              # Tier 3: Backup & Cloud
              restic          # Backup
              rclone          # Cloud storage

              # Setup & Pairing
              qrencode        # QR codes for mobile pairing
              zbar            # QR scanning (zbarimg)
              ffmpeg          # Camera preview + capture
              age             # Encryption for secrets
              sops            # Secret management

              # Development
              git
              neovim
              jq
              ripgrep
              fd

              # Nix tools
              nil             # Nix LSP
              nixpkgs-fmt     # Nix formatter
            ];

            shellHook = ''
              printf '\033[1m%s\033[0m\n' "Ultimate Notetaking, Sync & Backup System"
              echo ""
              echo "Get started:  ./setup"
              echo "Pair mobile:  ./setup mobile"
              echo "Sync:         ./scripts/usync"
              echo "Status:       ./scripts/ustatus"
            '';
          };
        }
      );

      # Export modules for use in other flakes
      nixosModules = {
        nb = import ./modules/nb.nix;
        syncthing = import ./modules/syncthing.nix;
        backup = import ./modules/backup.nix;
        default = { imports = sharedModules; };
      };

      # Templates for creating new hosts
      templates = {
        default = {
          path = ./templates/host;
          description = "Template for a new host configuration";
        };
      };
    };
}